Application programs running on different computers or nodes within a network are enabled to communicate and hence interoperate using messaging and queuing. Communication by messaging and queuing enables application programs to communicate across a network without having a private, dedicated, logical connection to link them. Application programs communicate by putting messages on message queues and by taking messages from message queues.
The application programs talk directly to a communications manager product such as a queue manager. Each node of the network has a queue manager which enables communication between the application programs running on the computers in different nodes of the network. The queue managers interface to the application programs through a message queue interface that is invoked by the application programs. The message queue interface supports many different operating system platforms enabling communication to be unaffected by the application programs operating on different operating systems.
Intercommunication means sending messages from one queue manager, known as the local or source queue manager, to another queue manager, known as the remote or target queue manager. The target queue manager could be running on the same platform as the source queue manager or could be on a different platform. This is called a distributed environment.
In prior art systems, distributed queuing works by a first application putting a message destined for an application governed by a remote queue manager, the local queue manager stores the message on a transmission queue, which is a queue on the local queue manager, until it is ready to send the message to the remote queue manager. The transmission queue is a type of local queue on which messages are stored before they can be successfully transmitted and stored on the remote queue manager.
Messages are transmitted between queue managers on a channel which is a one-way communication link between two queue managers. Software which handles the sending and receiving of messages is called a message channel agent (MCA). To send a message from queue manager A to queue manager B, a sending message channel agent on queue manager A must set up a communications link to queue manager B. A receiving message channel agent must be started on queue manager B to receive messages from the communication link. This one-way path consisting of the sending MCA, the communication link, and the receiving MCA is the channel. The sending MCA takes the messages from the transmission queue and sends them down the channel to the receiving MCA. The receiving MCA receives the messages and puts them on to the destination queues.
The sending and receiving MCAs can all run inside a channel initiator or mover which uses an address space under the control of the queue manager.
Queue managers which are logically associated in some way can be grouped in a cluster in which queues on each queue manager are available to every other queue manager in the cluster. Assuming they have the necessary network infrastructure in place, any queue manager in the cluster can send a message to any other queue manager in the cluster but this has conventionally relied on the standard distributed queuing mechanisms with the inherent overhead of establishing channel definitions before sending any data. Each queue manager in the cluster has a single transmission queue from which it can transmit messages to any other queue manager in the cluster. Each queue manager in the cluster needs to define one cluster-receiver channel and one cluster-sender channel.